Method for the catalytic conversion of alkylene carbonate

ABSTRACT

A method for catalytic conversion of alkylene carbonate, wherein alkylene carbonate is contacted with C 1 -C 5  aliphatic alcohol and/or water in the presence of Mg, Al mixed (hydr) oxide catalyst having a Mg:Al molar ratio in the range of from 4 to 20.

FIELD OF INVENTION

[0001] The present invention relates to a method for catalyticconversion of alkylene carbonate, using an Mg, Al mixed (hydr) oxidecatalyst, and a catalyst therefore.

BACKGROUND OF THE INVENTION

[0002] EP-A-0 51 351 disclose an Mg, Al mixed (hydr) oxide catalysthaving an Mg: Al molar ratio above 3 and preferably in the range from3-10.

[0003] The article of H. Schaper et al. in Applied Catalysis, 54, (1989)79-90, discloses the same catalyst. This catalyst has a hydrotalcitestructure, consisting of brucite type layers in which part of thebivalent ions (Mg) are replaced by trivalent ions, alternated byinterlayers which contain water and anions to compensate for the excesscharge of the trivalent ions. The preparation of such catalysts isdisclosed. Due to the basic properties such catalysts are considered ofspecial interest for base-catalyzed reactions, such as polymerization ofpropylene oxide, double-bond isomerisations of olefins such as1-pentene, and aldol condensations. Exemplified is double-bondisomerisation of 1-pentene using an Mg, Al mixed oxide catalyst havingan Mg:Al molar ratio of 5 and 10. At increasing molar ratio theconversion rate decreases.

[0004] The article of Watanabe, Y. et al. in Microporous and MesoporousMaterials 22 (1998) 399-407, discloses the use of Mg—Al hydrotalcitecatalysts having a molar ratio of 1.8-2.5 for the methanolysis ofethylene carbonate for the production of dimethyl carbonate.

[0005] EP-A-0,478,073 describes a process for preparing a dialkylcarbonate which comprises contacting an alkylene carbonate with analkanol in the presence of a mixed metal oxide catalyst or a modifiedbimetallic or polymetallic catalyst under conditions effective toproduce the dialkyl carbonate. In the examples, a magnesium/aluminiummixed metal oxide catalyst having a Mg:Al ratio of 3:1 was employed.

[0006] In JP-A-06/238165, a process is described wherein an alkylenecarbonate and an alcohol are subjected to transesterification inpresence of a catalyst to produce a dialkyl carbonate. A combination ofMagnesium oxide and another metal oxide other than magnesium was used ascatalyst in an atomic ratio in the range of 1000:1 to 20:1 of magnesiumto the other metal.

[0007] The present invention has for its object to provide a method forthe catalytic conversion of alkylene carbonate having an improvedconversion rate and improved yield, while having limited leaching ofmetal from the catalyst.

SUMMARY OF THE INVENTION

[0008] Accordingly, the invention provides a method for catalyticconversion of alkylene carbonate, wherein alkylene carbonate iscontacted with C₁-C₅ aliphatic alcohol and/or water in the presence ofMg, Al mixed oxide catalyst having an Mg:Al molar ratio in the range offrom 4 to 20.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0009] The invention is based on the insight that by increasing theMg:Al molar ratio in this type of (hydrotalcite) catalyst conversionrate and yield both improve. Although in the preparation of the catalysta so called mixed Mg/Al hydroxide is formed it might be that underworking conditions mixed Mg/Al oxides also or only are present. Thecatalyst will be referred to as Mg, Al (hydr)oxide catalyst. At molarratios above about 4, such as of from about 4 to about 20 Mg:Al and,preferably, above about 5 such as about 5 to about 20 the catalystexhibits the highest activity.

[0010] During the catalytic conversion of alkylene carbonate metaloxide, in particular Mg, may leach from the catalyst particles. Theleach rate is reduced when the Mg:Al molar ratio is below about 20, suchas of from about 4 to about 20, preferably below about 10, such as offrom about 4 to about 10. The MG,Al (hydr) oxide catalyst suitable forthe purpose of the present invention will therefore have a Mg:Al ratioof at least about 4, preferably more than about 4, even more preferablyat least about 5, and most preferably more than about 5. The Mg,Al(hydr) oxide catalyst will further preferably have a Mg:Al ratio of atmost about 20, more preferably of less than about 20, even morepreferably of at most about 15, again more preferably of less than about15, most preferably of at most about 10.

[0011] Alkylene carbonate suitable for use in the catalytic conversionmethod according to the invention may be a C₁-C₅ alkylene carbonate suchas 1,2 and 1,3 propylene carbonate, 1,2 and 2,3 butadiene carbonate.Preferred are ethylene carbonate and propylene carbonate. C₁-C₅aliphatic alcohol suitable for use comprises a straight and branchedC₁-C₅ alkanols. Preferred are methanol and ethanol. Most preferred ismethanol. In the presence of one or a mixture of C₁-C₅ alkanol, thealcoholysis results in the formation of di(C₁-C₅) alkyl carbonate andalkylene diol. In the presence of only methanol the methanolysis resultsin the formation of dimethyl carbonate and the alkylene diol. Thecatalytic conversion in the presence of only water results by hydrolysisin the production of the alkylene diol and carbon dioxide. The catalyticconversion in the presence of C₁-C₅ aliphatic alcohol and water resultsin the formation of all end products in ratio's dependent on themethanol:water molar ratio. When the molar ratio of methanol:water ishigher than about 6, such as from about 10 to about 20. The dimethylcarbonate:alkylene diol molar ratio is between about 1 and about 0.

[0012] Another aspect of the invention relates to the use of thiscatalyst as defined above for the catalyst conversion of alkylenecarbonate with C₁-C₅ aliphatic alcohol and/or water, and in particularto the methanolysis and/or hydrolysis of alkylene carbonate.

[0013] The Mg, Al mixed (hydr) oxide catalyst has generally a Mg:Almolar ratio in the range of of from about 4 to about 20. At higher molarratio's leaching of the metal oxide, in particular Mg increases. For anoptimal catalyst activity at low Mg leaching the Mg:Al molar ratio is inthe range of from about 4 to about 20, in particular of from about 5 toabout 10 or of from about 10 to about 20.

[0014] The method and use of the catalyst according to the inventionwill be further elucidated by reference to the following examples whichare provided for illustrative purposes and to which the invention is notlimited.

EXAMPLE 1 Catalyst Preparation

[0015] The Mg/Al samples were prepared by semi-batch co-precipitation atconstant pH. Aqueous solutions of Mg(NO₃)₂.6H₂O (1 M) andA1₂(SO₄)₃.18H₂O (0.5 M) were prepared from demineralised water and mixedproportionally to the targeted Mg/Al molar ratio. The resulting solutionwas then added drop-wise to 600 ml of an aqueous solution of 25% NH₃(pH=9) under constant stirring at 65° C. The precipitating solution waskept at pH=9 by addition of 25% NH₃ solution. The slurry was then agedfor 1 hour under continuous stirring and filtered. The resulting pastewas washed with demineralised-water until the pH of the wash waterbecame neutral and, finally, dried over night at 80° C.

EXAMPLE 2 Catalyst Screening

[0016] The samples were evaluated in a unit equipped with 6 quartzreactors having an inner diameter of 3 mm. Catalyst charges of 0.15 gram(30-80 mesh size) were diluted with 0.45 gram of SiC (0.05 mm diameter)and loaded into the reactor, with a pre-bed of 0.45 gram SiC placed ontop. The catalysts were dried in situ under N₂₋flow at 120° C. for 1hour. The reactors were then pressurised to 25-30 bar and the feed flowis started with a space velocity of WHSV=5 gr/(gr.hr), together with amoderate N₂ flow of WHSV=2 gr/(gr.hr). The liquid feed consisted of aPC:MeOH mixture of 1:4 molar ratio. After a stabilising period of 20hours at 120° C., the liquid products were condensed at 15° C. and 1 barduring a 24 hours run for off-line GC analysis. The moderate N₂ flowneeded for pressure regulation and product transport stripped some ofthe light ends from the sample. Therefore mass balances were only madeon propylene carbonate.

[0017] In the following examples, the conversion of methanol and yieldof dimethyl carbonate (DMC) are based on the molar amounts of thesecompounds divided by the molar amount of methanol supplied times 100%.The conversion of propylene carbonate to monopropyleneglycol (MPG)and/or methylpropanyl carbonate (MPC in mol %) and the yield of MPGand/or MPC are based on the molar amount of recovered PC divided by themolar amount of PC supplied in the feed times 100%. TABLE 1 performanceof Mg/Al (hydr) oxides for methanolysis of propene carbonate (120° C.,total liquid WHSV = 5 g/g/h, a N₂ flow of WHSV of 2 g/g/h and 25 bar,catalyst calcined at 400° C. unless specified otherwise) Conv. Yieldlight Catalyst MeOH^(a) PC^(b) DMC^(a) MPG^(b) ends^(b) MPC^(b)  1Mg/Al^(c) 8.9 12.4 1.7 6.4 0.3 5.9  2 Mg/Al 9.0 11.5 1.5 5.5 0.4 6.0  5Mg/Al 15.1 21.1 3.8 15.4 0.3 5.7 10 Mg/Al 17.4 25.3 4.7 20.2 0.4 5.1 20Mg/Al 26.0 35.8 8.3 34.1 0.1 1.6 50 Mg/Al 25.0 34.1 8.0 32.5 0.0 1.6 Mg(OH)₂ 6.6 8.6 1.8 7.0 0.0 1.6 Effect of calcinations  5 Mg/Al 15.1 21.13.8 15.4 0.3 5.7 calc. 400° C.  5 Mg/Al 16.6 23.4 4.35 18.2 0.4 5.1calc. 80° C. 10 Mg/Al 17.4 25.3 4.7 20.2 0.4 5.1 calc. 400° C. 10 Mg/Al15.7 21.0 4.0 15.9 0.3 5.1 calc. 80° C.

[0018] According to table 1, the activity of the mixed Mg/Al (hydr)oxides increases with increasing Mg/Al ratio, exception made for thepure Mg(OH)₂ which shows one of the lowest activity, possibly because ofleaching indicated by the formation of a hazy liquid product.

[0019] Calcining the materials at 80 or 400° C. prior to loading intothe reactor had little influence on their catalytic performance. Thisillustrated for 5 Mg/Al and 10 Mg/Al in Table 1.

[0020] The 20 Mg/Al and 50 Mg/Al catalysts exhibit the highest activity,but degrade to some extent during the reaction such that thecatalyst/SiC bed was very hard to remove from the reactor. By contrast,the other samples came out as free flowing particles. The Mg(OH)₂ samplewas also free-flowing, though the haziness of the liquid productsuggests significant leaching during the reaction.

[0021] Similar results have been obtained when using ethylene carbonate(EC) instead of propylene carbonate. Under the same operating conditionsas applied for the examples of table 1, except for the ethylenecarbonate which now substitutes the propylene carbonate in the feed, the5 Mg/Al catalyst converted EC to EG with 28 mole % yield based on ECsupplied in feed and a DMC/EG molar ratio of 0.89.

EXAMPLE 3 Catalyst Stability/Activity

[0022] In order to assess the stability of the various materials,samples of 0.1 g of each catalyst were immersed in 15 ml of arepresentative MeOH:PC:MPG mixture (3.46:0.88:0.24 molar ratio) for 20hours at room temperature. Then 5 ml samples were taken from the top ofthe liquid and analysed with ICP-spectrometry. The magnesium content ofthese products increased with the Mg/Al molar ratio starting at Mg/Al of˜10 (Table 2). It is concluded that the 5 Mg/Al and 10 Mg/Al catalystsoffer the best compromise between activity and stability in the reactionmedium. TABLE 2 Magnesium content of a MeOH:PC:MPG mixture(3.46:0.88:0.24 molar ratio) after 20 hours immersion of various Mg/Almixed hydroxide at room temperature. Mg leaching Catalyst [mg/kg] 1Mg/Al 9.30 2 Mg/Al 3.52 5 Mg/Al 10.14 10 Mg/Al 25.0 20 Mg/Al 34.5 50Mg/Al 72.9 Mg 164.4

EXAMPLE 4 Performance in Methanolysis/Hydrolysis

[0023] The catalytic tests were carried out in a single-tube microflowunit which is equipped with a HPLC pump to feed the PC-MeOH-watermixture, a gas manifold to introduce N₂ at 0.7 Nl/h, a traced feed line,a stainless steel reactor of 15 mm ID (with thermowell) operating indown flow, a high-pressure condenser operating at room temperature andan automatic sampling manifold that distributes the liquid productsequentially over six bottle of 300 ml.

[0024] The reactor was typically charged with 2 g of catalyst (1.6 mmcylinders) diluted in 15 g of SiC. Once loaded, the reactor was heatedup to reaction temperature (120-140° C.) under a N₂ flow of 0.7 Nl/h(i.e. WHSV of ˜0.4 g N₂/g cat/h) at 25-30 bar for 16 h. The reactor wasthen set to reaction temperature and pressure (25 bar), contacted withthe partially vaporised feed at target velocity (typically 2 g liq./gcat/h) and operated under varying conditions for more than 1000 hourswithout interruption.

[0025] The liquid product was analysed off-line by means of GC using thepolar column. The gas stream was not analysed. However, occasional useof a cold trap (−60° C.) in the gas line did not provide more than 0.05C % (based on total feed) of additional product, which appeared to bemainly methanol upon immediate GC analysis. TABLE 3 performance of 5Mg/Al (hydr) oxide for methanolysis and/or hydrolysis of propenecarbonate (140° C., total liquid WHSV = 2 g/g/h, a N2 flow of WHSV of0.4 g/g/h and 25 bar) Feed MeOH: Conv. Yield light DMC: H₂O:PC MeOH^(a)PC^(b) DMC^(a) MPG^(b) ends^(b) MPC^(b) MPG^(c) 4:0:1 22.6 39.7 8.7 34.10.7 2.3 1.0 1:0:1 22.8 11.6 10.6 10.0 0.3 1.4 1.1 0.5:0:1 28.1 6.3 12.65.4 0.3 0.6 1.1 4:0:1 22.6 39.7 8.2 34.1 0.7 2.3 1.0 3.8:0.2:1 7.4 36.33.5 35.0 0.1 1.3 0.4 3.4:0.6:1 1.4 52.2 0.5 50.8 0.0 1.4 0.0 0.5:0:128.1 6.3 12.6 5.4 0.3 0.6 1.1 0.3:0.2:1 2.4 21.1 0.5 20.6 0.0 0.4 0.00:0.36:1 — 35.1 — 35.1 0.0 0.0 0.0

[0026] Table 3 shows that the 5 Mg/Al catalyst converts PC to MPG in thepresence of methanol and/or water in varying ratio. The catalyst wasstable for more than 1000 h and operated satisfactorily over a widetemperature range, from 120 to 180° C. and a variety of residence time,from 4 to 40 min (1/WHSV). By varying the feed composition it producedDMC/MPG in a ratio that varied from nearly 1:1 with a water-free feed to0:1 with a methanol-free feed. The hydrolysis reaction turns out toproceed at higher rate than the methanolysis reaction (compare e.g. thefeed of 0:0.36:1 with 0.5:0:1, respectively). In contrast to thehydrolysis reaction, the methanolysis is limited by thermodynamicequilibrium. These two phenomena result in a DMC:MPG molar ratio in theproduct that drops much faster than do the MeOH:H₂O molar ratio in thefeed. In other words, it suffices to substitute as small fraction ofwater for MeOH to uncouple the production of DMC from that of MPG.

[0027] The spent catalyst did not significantly differ from the freshcatalyst as characterised by XRD, XPS and bulk element analysis. Theabsence of significant chemical changes of 5 Mg/Al catalyst during thereaction of PC with MeOH is consistent with the low Mg and Al content(<10 ppm) of the liquid product measured by means of ICP analysis. Whennormalised to the production rate of MPG, the Mg leaching rate generallyremained below 100 ppm (i.e. <100 mg Mg/kg MPG) and more typically <50ppm. This low leaching rate holds for MeOH:PC as well as H₂O;PC andMeOH:H₂O:PC feeds.

[0028] Similar results are obtainable with other alkylene carbonates andC₂-C₅ aliphatic alcohols.

1. A method for catalytic conversion of alkylene carbonate, whereinalkylene carbonate is contacted with (i) C₁-C₅ aliphatic alcohol, (ii)water, or (iii) a mixture (i) and (ii) in the presence of Mg, Al mixed(hydr) oxide catalyst having a Mg:Al molar ratio in the range of fromabout 4 to about
 20. 2. The method as claimed in claim 1, wherein theC₁-C₅ aliphatic alcohol is methanol or ethanol.
 3. The method as claimedin claim 1, wherein the Mg:Al molar ratio is above about
 4. 4. Themethod as claimed in claim 1, wherein the alkylene carbonate is ethylenecarbonate or propylene carbonate.
 5. A method for using a catalystcomprising a Mg, Al mixed (hydr) oxide catalyst having a Mg:Al molarratio in the range of from about 4 to about 20 for contacting alkylenecarbonate with (i) C₁-C₅ aliphatic alcohol, (ii) water, or (iii) amixture of (i) and (ii), wherein the molar ratio of C₁-C₅ aliphaticalcohol to water is below about
 20. 6. A process for producing di(C₁-C₅)alkyl carbonate and alkylene diol, which process comprises the steps ofcontacting alkylene carbonate with C₁-C₅ aliphatic alcohol in thepresence of a Mg, Al mixed (hydr) oxide catalyst having a Mg:Al molarratio in the range of from about 4 to about
 20. 7. A process forproducing alkylene diol and carbon dioxide, which process comprises thesteps of contacting alkylene carbonate with water in the presence of aMg, Al mixed (hydr) oxide catalyst having a Mg:Al molar ratio in therange of from about 4 to about
 20. 8. A product stream comprisingdi(C₁-C₅) alkylcarbonate and alkylene diol made by a process comprisingthe steps of contacting alkylene carbonate with C₁-C₅ aliphatic alcoholin the presence of Mg, Al mixed (hydr) oxide catalyst having a Mg:Almolar ratio in the range of from about 4 to about
 20. 9. A productstream comprising alkylene diol and carbon dioxide made by a processcomprising the steps of contacting alkylene carbonate with water in thepresence of a Mg, Al mixed (hydr) oxide catalyst having a Mg:Al molarratio in the range of from about 4 to about 20.